Many functions of modern devices in automotive, consumer and industrial applications, such as converting electrical energy and driving an electric motor or an electric machine, rely on semiconductor devices. Insulated Gate Bipolar Transistors (IGBTs) have been used for various applications including but not limited to switches in power supplies and power converters.
The direction of current flow through IGBTs operating as switches or motor drivers may be different in different operating cycles. In a “forward mode” of the IGBT, the pn-body diode at the body-drain junction of the IGBT is reversely biased and the resistance of the device can be controlled by the voltage applied to the gate electrode of the IGBT. To allow low ohmic current flow through the IGBT in a “reverse mode”, in which the pn-body diode is forwardly biased, a structured collector region having portions of both doping types may be provided. The loss of the thereby monolithically integrated free-wheeling diode is, in reverse mode of the IGBT, mainly determined by the product of current flow and voltage drop across the body diode. IGBTs with monolithically integrated free-wheeling diodes are also termed reverse conducting IGBTs. These semiconductor devices avoid inductances and capacitances associated with the required contacts and supply lines of external free-wheeling diodes.
For reasons of high latch-up robustness, a highly doped anti-latch-up region is typically provided in the body region of IGBTs. In reverse mode, the anti-latch-up region operates as emitter region with high emitter efficiency of the integrated free-wheeling diode. This results in flooding of the drift zone, which in the following is also referred to as a base region, with minority charge carriers during reverse mode of the IGBT. Accordingly, the reverse current peak, the switching-off energy of the integrated free-wheeling diode and the switching-on energy of the IGBT are often too high for IGBTs with monolithically integrated free-wheeling diode, in particular in hard-switching applications.
To reduce the flooding of the base region with minority charge carriers in reverse mode, the life time of the minority charge carriers may be reduced in the base region, for example by using rapid gold or platinum diffusion or by irradiating the semiconductor body of the IGBT during processing with high energetic particles such as electrons or protons. However, the reduction of charge carrier life time typically results both in an increased forward voltage VF and in an increased saturation forward voltage VCEsat. This in turn increases the power loss of the IGBT in forward mode.